The major goal of this study is to characterize the effects of the radiation- induced oxidative DNA lesion, 7,8-dihydro-8-oxoguanine (8-OH-G) on mutagenesis and killing in the bacterium, Escherichia coli. We propose a genetic approach, using the well-characterized mutT, mutM and mutY strains that are defective in particular steps in the prevention of repair of 8-OH-G DNA lesions. The oxidative damage will be generated by ionizing radiation (137Cs gamma rays) under aerobic and anaerobic conditions. Radiation-induced 8-OH-G DNA lesions will be quantitated by ELISA assay and comparisons of radiation effects will be made with studies of H2O2-induced oxidative damage. A secondary goal of this study will be to determine the efficacy of a nitrone spin trap agent, such as N-tert-butyl-alpha-phenylnitrone (PBN), in reducing the lethal and mutagenic effects of radiation in wild-type and repair-defective E. coli strains. PBN react with the OH. radical which allows an evaluation which allows an evaluation of the role of OH. producing in producing 8-OH-G DNA lesions.